Que3.5. Write short note on quality control of concrete.

Answer 1. The strength of concrete varies from batch to batch over a period of time. ue3.6. bandy the statistical quality control of concrete. Explain common language used in statistical quality control of concrete. Answer Statistical Quality Control of Concrete 1. Statistical quality control system provides a scientific approach to the concrete developer to understand the realistic variability of the accoutrements so as to lay down design specifications with proper forbearance to feed for necessary variations. 2. The acceptance criteria are grounded on statistical evaluation of the test result of samples taken at arbitrary during prosecution. By contriving a proper slice plan it’s possible to insure a certain quality at a specified rise. 3. therefore the system provides a scientific base of acceptance when is not only realistic but also restrictive as needed by the design conditions for the concrete construction. Common language The common languages that are used in the statistical quality control of concrete. 1. Mean Strength This is the average strength attained by dividing the sum of strength of all the cells by the number of cells. 2. friction This is the measure of variability or difference between any observed data from the mean strength. 3. Standard divagation i. This is the root mean square divagation of all the results, is denoted by ii. Standard divagation increases with adding variability. iii. The characteristics of the normal distribution wind are fixed by the average value and the standard divagation. 4. Measure of Variation It’s an indispensable system of expressing the variation of result. ii. It’s anon-dimensional measure of variation attained by dividing the standard divagation by the computation mean and is expressed as 2. The sources of variability in the strength of concrete may be considered due to variation in the quality of the element accoutrements , variations in blend proportions due to batching process, variations in the quality of batching and mixing outfit available, the quality of supervision and workmanship. 3. These variations are ineluctable during product to varying degrees. 4. Controlling these variations is important in lowering the difference between the minimal strength and characteristic mean strength of the blend and hence reducing the cement content. 5. The factor controlling this difference is quality control. 6. The degree of control is eventually estimated by the variation in test results generally expressed in terms of the measure of variation.

Que3.7. Step by step explain the American Concrete Institute system of blend design.

Answer Following are the way in American Concrete Institute system 1. Data to be Collected Fineness modulus of named fine total. ii. Unit weight of dry rodded coarse total. iii. Specific graveness of coarse and fine summations in SSD condition iv. immersion characteristics of both coarse and fine summations. Specific graveness of cement. 2. From the minimal strength specified, estimate the average design strength by using standard divagation. 3. Find the water/ cement rate from the strength and continuity points of view. Borrow the lower value. 4. Decide the maximum size of total to be used. Generally for RCC work 20 mm andpre-stressed concrete 10 mm size are used. 5. Decide plasticity in terms of depression for the given job. 6. The total water in kg/ m3 of concrete is determined, corresponding to the named depression and named maximum size of total. 7. Cement content is reckoned by dividing the total water content by the water/ cement rate. 8. elect the bulk volume of dry rodded coarse total per unit volume of concrete, for the particular maximum size of coarse total and fineness modulus of fine total. 9. The weight of CA per boxy cadence of concrete is calculated by multiplying the bulk volume with bulk viscosity. 10. The solid volume of coarse total in one boxy cadence of concrete is calculated by knowing the specific graveness of CA. 11. also the solid volume of cement, water and volume of air is calculated in one boxy cadence of concrete. 12. The solid volume of FA is reckoned by abating from the total volume of concrete the solid volume of cement, CA, water and entangled air. 13. Weight of fine total is calculated by multiplying the solid volume of fine total by specific graveness of FA.

Que3.9. What do you mean by Rheology of fresh concrete? Explain the parameters of Rheology.

Answer 1. Rheology It may be defined as the wisdom of the distortion and inflow of accoutrements , and concerned with connections between stress, strain, rate of strain, and time. 2. The term rheology deals with the accoutrements whose inflow parcels are more complicated than of simple fluids( liquids or feasts). Parameters of Rheology Following are the parameter of rheology 1. Stability It’s defined as a condition in which the aggregate patches are held in homogeneous dissipation by matrix, and arbitrary slice shows the same flyspeck size distribution during transportation, placing and contraction. ii. The stability of concrete is measured by its isolation and bleeding characteristics. 2. Mobility i. The mobility of fresh concrete is its capability to flow under instigation transfer, i.e., under mechanical stresses. The inflow is confined by cohesive, thick and frictional forces. ii. The cohesive force develops due to adhesion between the matrix and aggregate patches. It provides tensile strength of fresh concrete that resists isolation. iii. The density of the matrix contributes to the ease with which the aggregate patches can move and rearrange themselves within the matrix. iv. The internal disunion occurs when a admixture is displaced and the aggregate patches restate and rotate. v. The resistance to distortion depends on the shape and texture of the total, the uproariousness of the admixture, the water- cement rate, and the type of cement used. 3. Compactability i. It measures the ease with which fresh concrete is compacted. ii. Compacting correspond of expelling entangled air and displacing the aggregate patches in a thick mass without causing isolation. iii. Compactability is measured by the compacting factor test.

Que3.10. Describe the Bingham model of Rheology of fresh concrete.

Answer 1. The inflow geste of fresh concrete doesn’t conform to Newtonian liquid. 2. The rate of shear stress to shear rate isn’t constant but depends upon the shear rate at which it’s measured, and may also depend on the shear history of the concrete sample being delved . 3. still, at low shear rates that are important in practice, the geste can be represented by a straight line which doesn’t pass through- the origin, i.e., which has an intercept on the stress axis. 4. The intercept indicates the minimum stress below which no inflow occurs. 5. The fact that concrete can stand in a pile( as in the case of the depression test) suggests that there’s some minimum stress necessary for inflow to do at all. 6. The minimum stress is called yield stress and designated by the symbol therefore the simplest inflow equation of concrete illustrated in 3.10.1 can be written as 7. This fine relationship is called the Bingham model. 8. Bingham model relates the shear stress of the material expressed in terms of its cohesion to plastic density, and the rate at which the shear cargo is applied. 9. To establish a straight line, at least two points are needed. Consequently, the plasticity of concrete can not be defined by the single- point tests that determine only one parameter, i.e., produce only single point, and thus have to be used in combination with other tests to achieve a better understanding of concrete rheology. 10. For illustration, the Vee- Bee test can be used with compacting factor test to measure mobility and compactability.

Que3.11. Explain the affective factors of rheological parcels of concrete.

Answer Following are the affecting factors of rheological parcels of concrete 1. Mix Proportion A concrete blend having an redundant quantum of coarse total will warrant sufficient mortar to fill the void system, performing in a loss of cohesion and mobility. 2. thickness The thickness of concrete, as measured by the depression test, is an index of the relative water content in the concrete blend. 3. Hardening and harshening Elevated temperature, use of rapid-fire- hardening cement, cement deficient in gypsum, and use of accelerating cocktails, increase the rate of hardening which reduces the mobility of concrete. ii. The dry and pervious total will fleetly reduce plasticity by gripping water from the admixture or adding the face area to be bathe. 4. Aggregate Shape and Texture i. The rough and largely angular total patches will affect in advanced chance of voids being filled by mortar, taking advanced fine aggregate contents and similarly advanced water content. ii. also, an angular fine total will increase internal disunion in the concrete admixture and bear advanced water content than well- rounded natural beach. 5. Aggregate Grading A well- graded total gives good plasticity. These goods are lesser in the fine total than in coarse total. 6. Maximum Aggregate Size An increase in the maximum size of total will reduce the fine total content needed to maintain a given plasticity, and will thereby reduce the face area to be bathe. 7. cocktails The cocktails which have significant effect on the rheology of concrete are plasticizers andsuper-plasticizers, airentraining agents, accelerators and retarders.